#include <fstream>
#include <climits>
#include <queue>
using namespace std;

ifstream fin("deque.in");
ofstream fout("deque.out");

int main() {
    int n, k, value;
    fin >> n >> k;
    deque<int> mydeque;
    for (int i = 0; i < n; ++i) {
        fin >> value;
        mydeque.push_back(value);
    }
    long long sum = 0;
    int min_value = INT_MAX;
    for (int i = 0; i < k && mydeque.size() >= k; ++i) {
        if (mydeque[i] < min_value) {
            min_value = mydeque[i];
        }
        if (i == k - 1) {
            sum += min_value;
            mydeque.pop_front();
            i = -1;
            min_value = INT_MAX;
        }
    }
    fout << sum;
    return 0;
}